Interpretive Summary: Durum wheats with “waxy” or amylose-free and “partial waxy” (reduced amylose) starch were developed. The starch of such wheats possesses altered cooking properties. Starches isolated from waxy, partial waxy and normal types were compared to those of commercially available common wheat wild-type and waxy starches, and functionalities compared to blends (inter-granular variants) of durum waxy and wild-type starches of 0, 6, 12, 18, 24, & 30% amylose content. Starch particle size distributions of partial waxy and normal types were similar; the waxy samples had starch granule size. There were large differences in starch gel color and gel strength observed between the waxy samples and normal samples. Numerous differences were observed via Rapid-Visco Analysis (RVA), a technique that measures starch cooking properties under shear or mixing stresses. Pasting peak viscosity and breakdown, measures of starch thickness at various temperatures, were inversely proportional to % amylose. These observations indicate waxy samples would make excellent starch substrates for applications such soups and gravies. One partial waxy type, known as the Wx-B1 null, had final cooking viscosity that from that of all other blends and genotypes, demonstrating that amylose content variation within starch granules does not always mimic the effects observed in mechanical blends of similar amylose concentration. Through use of these genetically-controlled “partial waxy” (reduced amylose) lines, or via the blending of waxy and normal (wild-type) wheats, food processors can develop starches with a wide range of functional properties. The commercial availability of waxy wheat starch would present U.S. gluten protein manufacturers with a novel starch product, which, coupled with the extraction of vital gluten would present a unique product combination.

Technical Abstract:
Partial waxy (reduced-amylose) and fully waxy (amylose-free) tetraploid durum wheats (Triticum turgidum L. var. durum) were developed by introgression of null alleles at the Wx-A1 and Wx-B1 loci from common hexaploid wheat (T. aestivum L.). These genotypes were used to investigate the relationships between both intra- and inter-granular variation in amylose concentration and starch functionality. Starches isolated from each genotype (intra-granular amylose variants) were compared to those of commercially available hexaploid wild-type and waxy starches, and functionalities compared to blends (inter-granular variants) of durum waxy and wild-type starches of 0, 6, 12, 18, 24, & 30% amylose content. Starch particle size distributions were not significantly different amongst partial waxy and wild-type genotypes; waxy samples had significantly smaller mean starch granule size. Few significant differences for crystallite melting and related intrinsic heat by differential scanning calorimetry (DSC) were observed, and the detected differences in starch gel color or gel strength generally were observed for the waxy samples relative to wild-type. Numerous significant differences were observed via Rapid-Visco Analysis (RVA). Pasting peak viscosity and breakdown were inversely proportional to % amylose. Wx-B1 null final viscosity differed significantly from that of all other blends and genotypes, demonstrating that amylose content variation within starch granules does not always mimic the effects observed in mechanical blends of similar amylose concentration.